Networks that primarily utilize data link layer devices are often referred to as layer two (L2) networks. A data link layer device is a device that operates within the second layer of the Open Systems Interconnection (OSI) reference model, i.e., the data link layer. One example of a common L2 networks is an Ethernet network in which end point devices (e.g., servers, printers, computers) are connected by one or more Ethernet switches or other L2 network devices. The Ethernet switches forward Ethernet frames, also referred to as L2 communications or L2 packets to devices within the network. As the Ethernet switches forward the Ethernet frames the Ethernet switches learn L2 state information for the L2 network, including media access control (MAC) addressing information for the devices within the network and the physical ports through which the devices are reachable. The Ethernet switches typically store the MAC addressing information in MAC tables associated with each of their physical interfaces. When forwarding an individual Ethernet frame, an ingress port of an Ethernet switch typically multicasts the Ethernet frame to all of the other physical ports of the switch unless the Ethernet switch has learned the specific physical port through which the destination MAC address devices is reachable. In this case, the Ethernet switch forwards a single copy of the Ethernet frame out the associated physical port.
Some layer three (L3) networks that route communications at the third layer of the Open Systems Interconnection (OSI) reference model, i.e., the network layer, employ L3 network devices that also perform L2 functionality to bridge and switch L2 communications to other L3/L2 and L2 network devices within the networks. One mechanism by which network service providers that operate L3 networks provide L2 connectivity to their customers is by use of a virtual private local area network service (VPLS). A customer-specific VPLS instance transports layer two (L2) communications, such as Ethernet packets, between customer network sites through the service provider network core. In a typical configuration, provide edge (PE) routers coupled to the customer network sites define label switched paths (LSPs) that may be used to carry pseudowires that carry encapsulated L2 communications within the provider network as if the customer network sites were directly attached to the same local area network (LAN). Each of the PE routers operates as a virtual L2 switch having customer- and core-facing interfaces to connect the multiple LAN segments of an overall customer network defined by the individual customer network sites.